My main research question is, “How do hormones and growth factors regulate the proliferation activity of germ cells, in particular of spermatogonial stem cells?” Moreover, I am interested in the regulation of the production/release of pituitary hormones regulating spermatogenesis, in particular FSH.

The experimental models used to approach these questions are the zebrafish (Danio rerio), and in collaboration with other research groups (e.g., at the Institute of Marine Research in Bergen, Norway), also economically relevant species, such as the Atlantic salmon (Salmo salar).

The basic research concentrates on four aspects:

• identify candidate growth factors relevant for spermatogenesis via gene expression profiling (e.g. microarray; RNAseq [mRNA, miRNA, lncRNA]);
• characterize the biological activity of identified candidate factors by expression profiling (RNAseq), gain-of-function and loss-of-function approaches, often using a primary testis tissue culture system (e.g. pharmacological approaches; production of recombinant proteins; targeted gene knock out);
• study the endocrine regulation of expression and/or release of identified candidate factors;
• examine the endocrine regulation of pituitary FSH production and release.

Points 1-3 are mainly approached with the zebrafish model, points 2 (in part) and 4 (mainly) with the Atlantic salmon model.

The equilibrium between stem cell self-renewal and differentiation is also relevant for an applied research field we are interested in, aquaculture biotechnology. Sexual maturation or puberty poses significant economic, ecological, and animal welfare problems, for example for Atlantic salmon aquaculture. Puberty is associated with a switch from self-renewal to an increased differentiation of stem cells. Knowledge on the physiological mechanisms controlling the switch in stem cell activity is the basis for developing approaches to delay the start of pubertal testis maturation. In addition, sexually competent fish escaping from aquaculture facilities (e.g. after storm-induced damage) entail the risk of genetic introgression into native populations. Precocious male puberty and genetic introgression are two major problems creating obstacles for the further development of protein production for human consumption from salmon aquaculture.